linux-kernel - Re: [PATCH bpf-next 2/3] bpf: Add a BPF helper for getting the IMA hash of an inode

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Message-ID: <20201124040220.oyajc7wqn7gqgyib@ast-mbp>
Date:   Mon, 23 Nov 2020 20:02:20 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     KP Singh <kpsingh@...omium.org>
Cc:     James Morris <jmorris@...ei.org>, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, linux-security-module@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Florent Revest <revest@...omium.org>,
        Brendan Jackman <jackmanb@...omium.org>,
        Mimi Zohar <zohar@...ux.ibm.com>
Subject: Re: [PATCH bpf-next 2/3] bpf: Add a BPF helper for getting the IMA
 hash of an inode

On Fri, Nov 20, 2020 at 01:17:07PM +0000, KP Singh wrote:
> +
> +static bool bpf_ima_inode_hash_allowed(const struct bpf_prog *prog)
> +{
> +	return bpf_lsm_is_sleepable_hook(prog->aux->attach_btf_id);
> +}
> +
> +BTF_ID_LIST_SINGLE(bpf_ima_inode_hash_btf_ids, struct, inode)
> +
> +const static struct bpf_func_proto bpf_ima_inode_hash_proto = {
> +	.func		= bpf_ima_inode_hash,
> +	.gpl_only	= false,
> +	.ret_type	= RET_INTEGER,
> +	.arg1_type	= ARG_PTR_TO_BTF_ID,
> +	.arg1_btf_id	= &bpf_ima_inode_hash_btf_ids[0],
> +	.arg2_type	= ARG_PTR_TO_UNINIT_MEM,
> +	.arg3_type	= ARG_CONST_SIZE_OR_ZERO,
> +	.allowed	= bpf_ima_inode_hash_allowed,
> +};
> +
>  static const struct bpf_func_proto *
>  bpf_lsm_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>  {
> @@ -97,6 +121,8 @@ bpf_lsm_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>  		return &bpf_task_storage_delete_proto;
>  	case BPF_FUNC_bprm_opts_set:
>  		return &bpf_bprm_opts_set_proto;
> +	case BPF_FUNC_ima_inode_hash:
> +		return &bpf_ima_inode_hash_proto;

That's not enough for correctness.
Not only hook has to sleepable, but the program has to be sleepable too.
The patch 3 should be causing all sort of kernel warnings
for calling mutex from preempt disabled.
There it calls bpf_ima_inode_hash() from SEC("lsm/file_mprotect") program.
"lsm/" is non-sleepable. "lsm.s/" is.
please enable CONFIG_DEBUG_ATOMIC_SLEEP=y in your config.